Most people overlook this treatment when applying wall and floor tiles.
It is really important to understand whether the tile you have bought needs to be treated with a sealer to block the small particles in the surface of the tile.
Failure to treat a porous tile will result in the grout penetrating the tile surface leaving nasty stains that cannot be removed
There are various types of tile that are on the market available for you to tile your projects.
These types of tiles have a glass glaze on the top of the clay back which provides a non porous surface as the glass will not let anything penetrate it, unless it is un glazed.
There is no need to seal this tile.
A porcelain tile has been fired at a higher temperature than ceramics and this is called the vitrified process, this means these tiles are non absorbent on the front back or sides of the tile.
This is fine on most porcelain tiles but some porcelains have been mechanically polished to give a deep high shine, this leaves the surface of the porcelain tile to have tiny pours which the grout will penetrate. A sealer would need to be applied if it has a glossy look
Natural Stone Tiles
Most natural stone tiles are porous and are made from natural rock. When grout is applied to the surface of the tile to fill the joints it also penetrates the surface like polished porcelain above, this will also leave nasty marks on the stone that cannot be removed.
How to tell if a tile needs a sealant
The best way to check whether a tile is porous and will stain is to use a dry wipe whiteboard marker to test them.
In a small area of one tile apply the ink marker to a corner and leave for a few minutes, once done wipe off the ink, if there is a stain where the ink has penetrated the tile then the tiles will need sealing, if all the ink wipes off with no marks left then there is no need to seal.
The tile shops sell a range of sealers applicable to the type of tile you have bought, simply follow the instructions on the can, leave to dry and grout as usual.